If asked whether one would prefer to be too skinny or fat, chances are most people would reply that they’d rather be too skinny. Distorted standards of beauty and their propagation on social media are certainly to blame for this, in addition to the knowledge that being overweight typically brings along a host of health risks. A new study, however, suggests that being too thin can actually be deadlier.
Researchers used health data to investigate the relationship between body mass index (BMI) and mortality in 85,761 individuals, revealing that people can be “fat but fit.” They presented their results at the annual meeting of the European Association for the Study of Diabetes (EASD), which started today.
BMI measures fat based on height and weight and classifies individuals as underweight (less than 18.5), normal (18.5 to less than 25), overweight (25 to less than 30), obese (30 to less than 40), or severely obese (40 and over). In the research, scientists divided the normal range into lower normal (18.5 to <20), middle normal (20.0 to <22.5), and upper normal (22.5 to <25.0). 81.4% of the studied participants were female, and the median age was 66.4 years. Researchers accounted for sex, comorbidity level, and education level.
What BMI range has higher mortality?
“There are conflicting findings about the BMI range linked to lowest mortality,” Sigrid Bjerge Gribsholt, lead author of the research and a researcher at Aarhus University’s department of clinical medicine, said in a European Association for the Study of Diabetes statement. “It was once thought to be 20 to 25 but it may be shifting upward over time owing to medical advances and improvements in general health.”
7,555 (8%) of the participants died during the team’s five years of follow-up, and researchers compared the likelihood of mortality in different BMI ranges to that of people with a BMI in the upper normal level. Their results indicate that underweight individuals were 2.73 times more likely to die than upper-normal individuals. Lower-normal individuals were two times more likely to die, and middle-normal individuals were 27% more likely to die than upper-normal individuals. Interestingly, overweight individuals as well as individuals in the lower part of the obese range (30.0 to <35.0) were just as likely to die as upper-normal individuals.
Researchers sometimes call this being metabolically healthy or “fat but fit.” Individuals with a BMI between 35 and less than 40, however, were 23% more likely to die. Severely obese people (BMI of 40 and over) were 2.1 times more likely to die than upper-normal individuals. In other words, a high BMI was not linked to higher mortality until a score of 35, and even scores between 35 and <40 only had a slightly higher risk of death. The team found similar patterns of mortality in the relationship between BMI and obesity in different ages, sexes, and levels of education.
“In line with earlier research, we found that people who are in the underweight range face a much higher risk of death,” Gribsholt said. A possible explanation could be that some people lose weight from illness. “In those cases, it is the illness, not the low weight itself, that increases the risk of death, which can make it look like having a higher BMI is protective,” she admitted. However, “it is also possible that people with higher BMI who live longer—most of the people we studied were elderly—may have certain protective traits that influence the results.”
BMI doesn’t reveal everything
What’s more, fat distribution plays an important role in an individual’s health, said Jens Meldgaard Bruun, a co-author of the study and also a researcher at Aarhus University’s department of clinical medicine. “Visceral fat—fat that is very metabolically active and stored deep within the abdomen, wrapped around the organs—secretes compounds that adversely affect metabolic health,” he explained. As such, people with a BMI of 35 who are apple-shaped (with fat around their abdomen) may have adverse health conditions that don’t affect others also with a BMI of 35 but who have fat on their hips, backside, and thighs.
“It is clear that the treatment of obesity should be personalized to take into account factors such as fat distribution and the presence of conditions such as type 2 diabetes when setting a target weight,” Bruun concluded.
In a world ruled by social media and advertising-driven unrealistic body expectations, the study joins previous research trying to set the record straight on healthy body weight. What’s more, it highlights—again—that BMI scores alone don’t necessarily provide the full picture, though the scale seems to be accurate regarding American obesity.